Step 1: Divide the number into separate digits:
7710 => 7 7 1 0
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 7 => 0
7 to 1 => 6
1 to 0 => 1
0 to 7 => 7
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
0 => E
6 => N
1 => C
7 => N
Step 4: Combine the filters to a string:
E N C N = ENCN